In video coding, pictures can be intra-coded (I-frame), predicted (P-frame) or bi-directionally predicted (B-frames). Prediction of P- and B-frames is based on previously encoded/decoded reference frames, and therefore reference picture lists are provided: P-frames have one list (list0), and B-frames have two lists (list0, list1). Since reference pictures are required for decoding other pictures, they are stored after their own decoding. SVC provides reference picture list reordering (RPLR). Spatially scalable video coding (SVC) has a base layer (BL) and one or more enhancement layers (EL). Currently, EL UPDATE has just been removed from SVC, i.e. the EL has also hierarchical B-picture structure and temporally has very close syntax as the BL1.
Currently, JSVM2 addresses forced RPLR commands to specify the real reference picture lists, rather than just utilize the default reference picture list construction process defined in chapter 8.2.4.2 “Initialisation process for reference picture lists” of the AVC3 specification and 8.2.4.2 of SVC working draft (WD).
In the case that BL and spatial EL have the same frame rate, actually the same RPLR commands should be used for both layers at the encoder. However, in the case that the EL frame rate is twice the BL frame rate, the RPLR commands are different.